People usually have only one key to open a door lock. After the key is lost or, for any reason, loaned or given to another person, such as a nurse, a relative, a tenant, or a maintenance worker, the house owner may worry about the integrity of the door lock. Currently, one's only remedy is to have the door lock replaced or rekeyed in order to have a new key. Nowadays, in hotels, apartments, and office buildings, locks with multiple keys are also used. However, the owner cannot selectively allow only one key to open the lock and not the other keys.